Deep-drawing magnesium-base alloy sheet



March 5, 1946. D. w. WATTERS 2,396,218

DEEP-DRAWING MAGNESIUM-BASE ALLOY SHEET Filed Oct. 7, 1942 Coo/[n 2 Wafer 6 60.5 Emmer 2 Oraw 2/22;

4M0gnes/Z/m Ease AV/qy J/vee/ 5 60.5 faumer I N V EN TOR. 0000/0 W Waffe/is ATY OLMEYS Patented Mar. 5, 1946 DEEP-DRAWING MAGNESIUM-BASE ALLOY SHEET Donald W. Watters, Mount Pleasant, Mich.. as-

signor to The land, Mich.,

Dow Chemical Company, Mida corporation of Michigan Application October 7, 1942, Serial No. 461,187

(Cl. 1135l) 4 Claims.

This invention relates to an improvement in the deep-drawing of magnesium-base alloy sheet.

The fabrication of a variety of ultra-light airplane parts is most successfully accomplished by operations involving the deep-drawing of formable magnesium-base alloy sheet. As is known, this material is drawn by procedures which in general resemble those used with steel, with the outstanding difierence that magnesium-alloy sheet is maintained at an elevated temperature, usually well above 400 F., during the drawing operation. Even under Optimum conditions, however, it has heretofore not been possible to form magnesium-alloys into objects in the making of which the drawing operation requires a draw-reduction appreciably above 60 per cent.

In addition, when operating at reductions approaching the 60 per cent limit, the physical properties of the drawn object, particularly its strength, have sometimes been undesirably low, presumably as a result of strains developed in the metal during drawing. In view of these factors, the fabrication of magnesium-alloys b deepdrawing, a method which would otherwise seem to be of extremely wide applicability, has in fact been restricted to the manufacture of objects which can be formed with roughly 50 per cent or less.

The principal object of the present invention, then, is to provide an improvement in the existing procedures for deep-drawing formable magnesium-base alloy sheet which renders possible draw-reductions of as high as 65 to 75 per cent or more without rupture of the sheet or appreciable decrease in its physical properties during the drawing operation.

The invention depends upon the discovery that while it is essential that any individual portion of the magnesium-base alloy sheet being deepdrawn by means of a die, draw-ring, and punch be at a temperature above 400 F. prior to and during the actual entry of that portion of the sheet into the die, very advantageous results are obtained when each portion of the sheet is rapidly chilled to a temperature below 200 F. immediately after its passage through the die and is maintained at such temperature throughout drawing. This cooling in some manner strengthens the sheet following its shaping by the die, preventing rupture or serious decrease in thickness of the shaped portions as the drawing continues, and also preserves or even improves the pre-existing physical properties of the metal. Because of these latter efiects, far greater drawreductions are possible than heretofore, and

a draw-reduction of many deep-drawn articles which previously could not be made may easily be formed.

. Deep-drawing of magnesium-base alloy sheet according to the invention is ordinarily accomplished with conventional equipment including die, draw-ring, and punch, the sheet to be formed being held tightly between the die and draw-ring. The sheet is heated, either in a preliminary step or better by heating the die and draw-ring, to bring it to a temperature above 400 F., after which the punch is actuated to force the heated sheet through the die. Special means are provided to insure that each portion of the sheet immediately after its passage through the die is chilled rapidly to a temperature below 200 F., therebyachieving the advantages set forth above.

Any of a variety of cooling methods may be employed to chill the heated sheet as it passes from the die, as, for example, by directing a cold fluid against the sheet just below the die orifice. In ordinary operation, however, the most effective chilling oi the sheet after deformation in the die is achieved simply by cooling the punch throughout drawing to a temperature well below 200 F., as by blowing cold air on it or circulating cooling fluid through it. This punch is, or course, in intimate contact with every portion of the sheet which has passed through the die, and serves effectively to chill the sheet to below 200 F. and maintain it at that temperature as drawing proceeds.

While the essence of the present improved deep-drawing method lies in the careful control .of the temperature of the sheet both before and after its passage through the die, it should be obvious that best results will be obtained only when the drawing equipment is otherwise carefully designed and operated in accordance with the best of current practice. Details of die construction and drawing procedures which should be observed with magnesium-alloys are given at length in the Journal of the Aeronautical Sciences, vol. 8, No. 1, pages 26-29 (Nov., 1940).

The process of the invention may advantageously be applied in all deep-drawing operations involving formable magnesium-base alloys, since the chilling of the sheet to below 200 F. improves the physical properties of the drawn product to values well above those obtained by conventional drawing. The new method is particularly valuable, as already noted, in making objects in which the draw-reduction required exceeds per cent (such draw-reduction being measured by the ratio of the difference between the diameter of the blank sheet D and the diameter of the drawn object d to the diameter of the blank sheet D, i. e. D-d) D Reductions of this magnitude have not been possible by previous drawing procedures.

The new process is useful, so far as known, in the deep-drawing of all formable magnesiumbase alloys. From a commercial viewpoint, it is most frequently applied to magnesium-base alloys containing 1 to 2 per cent by weight of manganese as the major alloying element. Such alloys should preferably be worked with an initial sheet temperature of 500 to 700 F.

The invention may be further explained with reference to the accompanying drawing, which illustrates diagrammatically, in vertical partial section, one form of apparatus for deep-drawing magnesium alloys.

The apparatus consists of a die I, draw-ring 2, and punch 3, which are actuated in conventional manner by means not shown. In operation, a magnesium-base alloy blank sheet 4 to be drawn is centered on the die and clamped securely by force applied to the draw-ring. Gasring burners 5 and 6 are then adjusted to heat the die and draw-ring to a temperature such that the sheet 4 is rapidly heated to and maintained at a temperature above 400 F. At the same time the punch 3 is cooled to a temperature well below 200 F. by circulating cooling water through a conduit 1 formed in the body of the punch. When the temperatures have been reached, the punch 3 is actuated to force the blank 4 through the die orifice, as shown in the drawing. By this procedure, all portions of the sheet enter the die at a temperature above 400 F. and as formed are rapidly chilled by the punch to a temperature below 200 F.

The following example will illustrate the invention, but is not to be construed as limiting its scope:

Example 1 An airplane nose-spinner was to be deep-drawn from an annealed sheet formed of a magnesiumbase alloy containing approximately 1.5 per cent manganese and 0.1 per cent calcium, balance magnesium, this sheet prior to drawing having physical properties as follows: tensile strength, 34,000 pounds per square inch; yield strength, 18,000 pounds per square inch; elongation in 2 inches, 17.2 per cent. The draw-reduction required was 65 per cent. When attempt was made to draw the spinner in conventional manner, with the sheet, die, and draw-ring maintained at a temperature of about 600 F. and the punch not positively cooled, it was determined that a draw reduction of 65 per cent was not possible without rupture of the sheet.

However, when a blast of cold air was directed onto the punch to maintain it at a temperature of about 100 F. throughout the drawing operation, (die, draw-ring, and sheet before entry into the die still being maintained at about 600 F.), drawing was accomplished with no difficulty.

The metal of the drawn spinner exhibited properties as follows: tensile strength, 40,600 pounds per square inch; yield strength, 31,000 pounds per square inch; elongation in 2 inches, 9.0 per cent. The essential physical characteristics of the metal were actually improved by the drawing operation.

Other modes of applying the principle of the invention may be employed instead of those described, change being made as regards details,

.provided the step or steps recited in any of the 400 F. and 700 F. is forced through a die, the

improvement which comprises cooling each portion of the sheet immediately after its passage through the die to a temperature below 200 F.

2. In a process for deep-drawing formable magnesium-base alloys by forcing a sheet thereof through a die to eiifect a draw reduction of at least 65 per cent, the method of preventing rupture of the sheet during drawing and obtaining high physical properties in the drawn product which comprises maintaining all portions of the sheet prior to entry thereof into the die at a temperature between 400 F. and 700 F. and ripidly cooling each portion of the sheet immediately after its passage through the die to a temperature below 200 F.

3. In a process for deep-drawing sheet formed of a magnesium-base alloy containing 1 to 2 per cent by weight of manganese as the major alloying element by forcing the sheet through a die to efiect a draw reduction of at least 65 per cent, the method of preventing rupture of the sheet during drawing and obtaining high physical prop- .erties in the drawn product which comprises maintaining all portions of the sheet prior to entry into the die at a temperature in the range 500 to 700 F. and rapidly cooling each portion of the sheet immediately after passage through a die to a temperature below 200 F.

4. In a process for deep-drawing formable magnesium-base allow sheet by means of a die, drawring, and punch, with the sheet held tightly between the die and the draw-ring, the improvement which comprises heating the die and drawring to an extent sufficient to maintain all portions of the sheet prior to entry thereof into the die at a temperature between 400 F. and 700 F. and then operating the punch to move it and a portion of the sheet through and beyond the opening in the die, while maintaining at the above-stated temperature that portion of the sheet within the opening, and then rapidly cool ing the said portion of the sheet immediately after passage through said opening to a temperature below 200 F. throughout the drawing operation.

DONALD W. WA'ITERS. 

